Patients who were screened for polyostotic fibrous dysplasia and MAS under NIH protocol 98-D-0145 and were found to have MAS with excess growth hormone are eligible for this 36-week study. The screening protocol includes a history and physical examination, blood and urine tests, hearing, eye and dental examinations, pain and physical function evaluations, endocrine and bone screening tests, various bone imaging studies, including magnetic resonance imaging (MRI) and computed tomography (CT) scans and bone biopsy in patients over 6 years old.